This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-291291, filed Sep. 25, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a cooling unit used to cool a heat generating component such as a semiconductor package, a circuit module including the cooling unit, and an electronic apparatus such as a portable computer mounted with the circuit module.
2. Description of the Related Art
An electronic apparatus such as a portable computer is furnished with an MPU (Micro Processing Unit) for processing multimedia information, including text, speech, and animations. The amount of heat released from the MPU of this type tends to increase rapidly during operation as its processing speed and the number of its functions increases. In order to ensure stable operation of the MPU, therefore, the heat radiating properties of the MPU must be improved. To attain this, the MPU requires use of a radiating component such as a heat pipe for discharging its heat to the outside.
A conventional heat pipe has an outer pipe in which a liquid refrigerant is sealed. The outer pipe is formed of a hard metallic material. Thus, if the heat pipe is directly affixed to the MPU, it cannot enjoy good adhesion to the MPU, so that heat from the MPU cannot be efficiently transmitted to the heat pipe. Conventionally, therefore, a soft heat conduction sheet or thermally conductive grease is sandwiched between the MPU and the heat pipe.
The heat conduction sheet is formed of a soft rubberlike elastic body having high heat conductivity. When the MPU and the heat pipe are connected thermally to each other, the heat conduction sheet is deformed so as to compensate for lowering of the heat conductivity that is attributable to the surface roughness of the two elements or absorb a gap that hinders heat conduction. In consequence, the thermal resistance of a thermal junction between the MPU and the heat pipe is lowered, so that the heat from the MPU can be efficiently transmitted to the heat pipe.
According to the conventional arrangement, however, the heat from the MPU is transferred to the refrigerant in the outer pipe after it is transmitted from the heat conduction sheet to the outer pipe. Accordingly, the outer pipe and the heat conduction sheet are inevitably interposed between the MPU as a heat source and the refrigerant that receives the heat, and cause a heat transfer loss. In consequence, the quantity of heat that can be transmitted from the MPU to the refrigerant is limited.
Higher-speed multifunctional versions of MPUs for portable computers are expected to be developed in the near future, and the amount of heat released from the MPUs is supposed to increase considerably. According to the conventional structure for thermal connection that uses the heat conduction sheet, therefore, there is a possibility that the cooling performance of the MPUs satisfactory or is limited. Thus, in consideration of the increase in the heat release value of modern MPUs, the rate of conduction of heat from the MPU is not to the refrigerant must be improved.
The present invention has been contrived in consideration of these circumstances, and its object is to provide a cooling unit, circuit module, and electronic apparatus, designed so that heat from a heat generating component can be efficiently transmitted to a refrigerant and the cooling performance of the heat generating component can be improved.
In order to achieve the above object, a cooling unit according to a first aspect of the present invention comprises a vessel filled with a refrigerant. The vessel includes a heat receiving portion for receiving heat from a heat generating component, a heat dissipating portion for dissipating the heat from the heat generating component, and a heat transfer portion for transferring the heat from the heat generating component, transmitted to the heat receiving portion, to the heat dissipating portion via the refrigerant. That part of at least the heat receiving portion of the vessel which receives the heat from the heat generating component is formed of a soft heat conduction sheet capable of elastic deformation, the heat conduction sheet being directly in contact with the heat generating component.
In order to achieve the above object, a cooling unit according to a second aspect of the invention comprises a heat receiving portion for receiving heat from a heat generating component, a heat dissipating portion for dissipating the heat from the heat generating component, and a heat transfer portion for circulating a refrigerant between the heat receiving portion and the heat dissipating portion and transferring the heat from the heat generating component, transmitted to the heat receiving portion, to the heat dissipating portion via the refrigerant. That part of at least the heat receiving portion which receives the heat from the heat generating component is formed of a soft heat conduction member capable of elastic deformation, the heat conduction member being directly in contact with the heat generating component.
In order to achieve the above object, an electronic apparatus according to a third aspect of the invention comprises a housing having a heat generating component therein and a cooling unit held in the housing. The cooling unit includes a heat receiving portion for receiving heat from the heat generating component, a heat dissipating portion for dissipating the heat from the heat generating component, and a heat transfer portion for transferring the heat from the heat generating component, transmitted to the heat receiving portion, to the heat dissipating portion via a refrigerant. That part of at least the heat receiving portion of the cooling unit which receives the heat from the heat generating component is formed of a soft heat conduction sheet capable of elastic deformation, the heat conduction sheet being directly in contact with the heat generating component.
According to this arrangement, the soft heat conduction sheet can be deformed into any desired shape. Therefore, it can adhere to the heat generating component so as to compensate for lowering of the heat conductivity that is attributable to the surface roughness of the heat generating component or absorb a gap that hinders heat conduction. Accordingly, only the heat conduction sheet is interposed between the heat generating component and the refrigerant, so that the thermal resistance of a heat conduction path that extends from the heat generating component to the refrigerant can be lowered. Thus, the heat transmitted from the heat generating component to the heat conduction sheet can be efficiently transferred to the refrigerant.
In order to achieve the above object, a cooling unit according to a fourth aspect of the invention comprises a thermally conductive main body including a heat receiving portion for receiving heat from a heat generating component and a heat dissipating portion connected thermally to the heat receiving portion, a fan for supplying cooling air to the heat dissipating portion, and a refrigerant passage in the main body for moving a liquid refrigerant between the heat receiving portion and the heat dissipating portion. The refrigerant passage transfers the heat from the heat generating component, transmitted to the heat receiving portion, to the heat dissipating portion via the refrigerant. That part of the refrigerant passage which corresponds to the heat receiving portion is formed of a soft heat conduction sheet capable of elastic deformation. The heat conduction sheet is directly in contact with the heat generating component.
In the arrangement described above, the heat transmitted from the heat generating component to the heat receiving portion is diffused by heat conduction to the heat dissipating portion and transferred from the heat receiving portion to the refrigerant in the refrigerant passage. Since the heat dissipating portion is compulsorily cooled with the cooling air, there is a great difference in temperature between the heat dissipating and receiving portions. Thus, the refrigerant heated in the heat receiving portion is reduced vapor and flows through the refrigerant passage toward the heat dissipating portion. Then, the vapor is condensed by heat exchange in the heat dissipating portion. The refrigerant that is liquefied by this condensation is returned through the refrigerant passage to the heat receiving portion by capillarity and subjected again to the heat from the heat generating component. By repeating this cycle, the heat from the heat generating component can be transferred from the heat receiving portion to the heat dissipating portion and emitted from the heat dissipating portion.
According to this arrangement, the soft heat conduction sheet can be deformed into any desired shape. Therefore, it can adhere to the heat generating component so as to compensate for lowering of the heat conductivity that is attributable to the surface roughness of the heat generating component or absorb a gap that hinders heat conduction. Accordingly, only the heat conduction sheet is interposed between the heat generating component and the refrigerant, so that the thermal resistance of a heat conduction path that extends from the heat generating component to the refrigerant c a n be lowered. Thus, the heat transmitted from the heat generating component to the heat conduction sheet can be efficiently transferred to the refrigerant.
In order to achieve the above object, a circuit module according to a fourth aspect of the invention comprises a circuit board having a mounting surface, a heat generating component mounted on the mounting surface of the circuit board, and a cooling unit for cooling the heat generating component. The cooling unit includes a heat receiving portion for receiving heat from the heat generating component, a heat dissipating portion for dissipating the heat from the heat generating component, and a heat transfer portion for transferring the heat from the heat generating component, transmitted to the heat receiving portion, to the heat dissipating portion via a refrigerant. That part of at least the heat receiving portion of the cooling unit which receives the heat from the heat generating component is formed of a soft heat conduction sheet capable of elastic deformation. The heat conduction sheet has an outer peripheral portion projecting around the heat generating component, the outer peripheral portion being directly in contact with the mounting surface of the circuit board.
According to this arrangement, the soft heat conduction sheet can be deformed into any desired shape. Therefore, it can adhere to the heat generating component so as to compensate for lowering of the heat conductivity that is attributable to the surface roughness of the heat generating component or absorb a gap that hinders heat conduction. Accordingly, only the heat conduction sheet is interposed between the heat generating component and the refrigerant, so that the thermal resistance of a heat conduction path that extends from the heat generating component to the refrigerant can be lowered. Thus, the heat transmitted from the heat generating component to the heat conduction sheet can be efficiently transferred to the refrigerant.
Besides, the outer peripheral portion of the heat conduction sheet is deformed and adheres to the mounting surface of the circuit board so as to fill the gap between the outer peripheral edge of the heat generating component and the mounting surface when the refrigerant is expanded by the heat from the heat generating component. Therefore, some of the heat delivered from the heat generating component to the circuit board can be transferred directly to the refrigerant through the heat conduction sheet. In consequence, much of the heat from the heat generating component can be absorbed efficiently, and temperature increase of the circuit board can be restrained.
In order to achieve the above object, a circuit module according to a sixth aspect of the invention comprises a heat generating component and a cooling unit for cooling the heat generating component. The cooling unit includes a heat receiving portion for receiving heat from the heat generating component, a heat dissipating portion for dissipating the heat from the heat generating component, and a pipeline for transferring the heat from the heat generating component, transmitted to the heat receiving portion, to the heat dissipating portion via a refrigerant. The heat receiving portion of the cooling unit is formed of a soft heat conduction pouch capable of elastic deformation and having a socket at one end thereof to which the pipeline is connected, the heat conduction pouch being directly in contact with the heat generating component.
According to this arrangement, the heat receiving portion is smoothly elastically deformed following the shape of the heat generating component and adheres to the heat generating component so as to absorb a gap that hinders heat conduction. Therefore, the heat transmitted from the heat generating component to the heat receiving portion can be transferred directly to the refrigerant. Thus, the thermal resistance of a heat conduction path that extends from the heat generating component to the refrigerant can be lowered, and the heat from the heat generating component can be efficiently transferred to the refrigerant.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.